If the split isn't too bad you can try cutting 75 to 100 mm off the mast without affecting its bend characteristics too much.Just add 75 too 100mm to your mast extension when rigging up.
If the split continues past the area you just cut off then basically all is lost as the stresses at the joint are extreme under load and a fiberglass epoxy repair wouldn't stand the strain anyway.
Good Luck,Fullmoon.